The present invention relates to a control arrangement for a reversible hydrostatic axial or radial piston machine, which mainly comprises a fluid guiding outer annular space surrounding a control body which is constituted by an eccentric disk connected to the shaft of the machine for rotation therewith and an inner control ring which is freely turnable on the periphery of the disk, as well as an outer control ring which is telescopingly and sealingly guided on the inner control ring, in which the rings are hydraulically and by a spring pressed apart in axial direction, with one of the control rings engaging with an end face thereof a planar control face of the machine and the other of the control rings engaging with an end face thereof a planar support face, which is axially spaced from and parallel to the planar control face. The eccentric disk has a hub surrounding the shaft and being provided with an end face which, supported by the force of a spring, is hydraulically pressed against the control face, whereby the disk, with the end face on its hub, and one of the control rings, with its end face pressed against the support face, limit a fluid guiding inner annular space which is sealed toward the shaft.
In a known construction of a control arrangement of the aforementioned kind, the commutation of the fluid is provided by means of a telescopic ring arrangement supported by a roller bearing and translatory moved by an eccentric disk. Characteristic for this construction are two annular spaces which are sealed against each other by the control rings and which are flown through by the fluid, whereby in the inner annular space a roller bearing is arranged which maintains a distance between the inner control ring and the eccentric disk. This known construction operates successfully since the friction losses produced thereby are very small so that the wear of this arrangement is practically zero, resulting in a long operating life thereof. This known arrangement may further be used with high fluid pressures, a high number of revolutions per minute and with high temperatures. In addition, it is not detrimentally influenced by temperature shocks or by fowling of the fluid.
Despite these, for the practical operation of this arrangement, favorable conditions, the known control arrangement has still some characteristics which could be improved and which limit the use of the arrangement. One of these characteristics is the necessity of a relatively large number of auxiliary parts for the sealing of the annular spaces and for movement of the control rings, which auxiliary parts have in addition to be manufactured to very close tolerances. Additional auxiliary parts with close tolerances evidently increase the cost of manufacturing of such a control arrangement and which correspondingly decrease considerably the commercial use thereof. If large fluid streams have to be guided through this known control arrangement with acceptable losses, then a further characteristic thereof is, that depending on the size of the arrangement, relatively large axially and radially extending mounting spaces are required. In addition, in the known control arrangement it is not possible to seal the eccentric disk towards a leakage space in such a manner, that according to the laws of hydrostatics an actually sufficient seal with the smallest possible friction can be derived.
It is further of importance in such control arrangements according to the prior art, that, in addition to the presence of a great number of high pressure seals, a roller bearing, flown through by fluid, is provided in the inner annular space between the eccentric disk and the inner control ring. Such a roller bearing, regardless of what construction, requires not only a relatively large mounting space, whereby the dimensions of the control arrangement, and therewith those of the complete machine, are increased, but such a roller bearing produces also very high losses in the fluid stream. Such losses will result in the transformation of a part of the energy input in heat, which will result in an increase of the operating temperature and a considerable change in the viscosity of the hydraulic fluid. This will result in a power loss so that at an acceptable efficiency of the machine the upper limit of the revolutions thereof is restricted.